May 20, 2015

Introducing Washington's first dinosaur

The fossil is a partial left thigh bone of a theropod dinosaur, the group of two-legged, meat-eating dinosaurs that includes Velociraptor, Tyrannosaurus rex and modern birds. It was found along the shores of Sucia Island State Park in the San Juan Islands.

The fossil is approximately 80 million years old and is from the Late Cretaceous period. During that time, the rocks that today form Sucia Island were likely further south. How much further south is a topic of scientific debate, with locations ranging between present day Baja California, Mexico, and northern California. Earthquakes and other geologic forces that constantly reshape our planet moved the rocks north to their present-day location.

The road to discovering Washington’s first dinosaur fossil...
On April 10, 2012, two Burke Museum research associates were at Sucia Island State Park with a collecting permit for fossil ammonites—sea creatures with spiral-shaped shells that lived at the same time as dinosaurs.

The shore where the fossil was found on the southwest tip of Sucia Island State Park. Photo courtesy of the Burke Museum.

While scanning the ground for ammonites, they spotted this.

The exposed bone sticks out of the rocky ground.
Photo courtesy of the Burke Museum.

Most people would have walked right by it. But our keen-eyed paleontologists could tell it was a small section of exposed bone. Since it was embedded in rock, they took photos, recorded the location and contacted our partners at Washington State Parks.

Dr. Adam Huttenlocker, at the time a University of Washington graduate student,
examines the first dinosaur fossil found in Washington state.
Photo courtesy of the Burke Museum.

The following month, a crew of Burke paleontologists returned to Sucia Island with permits to excavate the fossil so it could be studied. The shoreline where the fossil was found is now covered by landslides, so it is very fortunate that the Washington State Parks and the Burke Museum were able to excavate the fossil when they did!

Burke Museum paleontologists carefully excavate a section of rock
containing the fossil to prepare back at the Burke Museum.
Photo courtesy of the Museum.

Over the next year, Burke paleontologists worked to carefully remove the extremely hard rock surrounding the fossil so they could get a better look at the specimen.

It took nearly a year to remove the extremely hard rock and glue the fossil back together.
Photo courtesy of the Burke Museum.

Dr. Sidor and Peecook compared the fossil to other museums’ specimens and identified it as a partial left femur (thigh bone) of a theropod dinosaur, the group of two-legged, meat-eating dinosaurs that includes Velociraptor and Tyrannosaurus rex, and even modern birds. “This fossil won’t win a beauty contest,” Sidor said. “But fortunately it preserves enough anatomy that we were able to compare it to other dinosaurs and be confident of its identification.”

Dr. Christian Sidor (right), Burke Museum curator of vertebrate paleontology,
and Brandon Peecook (left), University of Washington graduate student,
show the size and placement of the fossil fragment compared to the
cast of a Daspletosaurus femur. Photo courtesy of the Burke Museum.

Although incomplete, Sidor and Peecook were able to determine the femur is from a theropod dinosaur for two reasons: 1) The hollow middle cavity of the bone (where marrow was present) is unique to theropods during this time period, and 2) A feature on the surface of the bone (the fourth trochanter) is prominent and positioned relatively close to the hip, which is a combination of traits unique to some theropod dinosaurs.

The first dinosaur fossil described from Washington state is a portion
of the femur (thigh bone) from a theropod dinosaur. The detailed
illustration shows the fourth trochanter highlighted in blue.
Illustration courtesy of PLOS ONE, modified by the Burke Museum.

The fossil is 16.7 inches long and 8.7 inches wide. Because it is incomplete, they aren’t able to identify the exact family or species it belonged to. However, Dr. Sidor and Peecook were able to calculate that the complete femur would have been more than three feet long—slightly smaller than T. rex.

The first dinosaur fossil bone discovered in Washington
state (bottom) sits next to the cast of a complete Daspletosaurus femur.
Photo courtesy of the Burke Museum.

We also learned that the fossil is from the Late Cretaceous period and is approximately 80 million years old, based on the age of the marine sediment that surrounded the fossil. This rocky matrix was filled with the fossil remains of tiny sea creatures. So, how did this dinosaur end up in the ocean?

Tiny fossil shells are still attached to the first dinosaur fossil found
in Washington state. Photo courtesy of the Burke Museum.

These clams found with the bone held the answer. They’re so well preserved we can tell they’re a species that lived in shallow water. So it’s likely that after the dinosaur died, its carcass was tossed by the waves and eventually came to rest on the seafloor among these clams. The rest of the dinosaur was likely washed away or carried away by scavengers.

The accompanying fossilized clams are so well preserved
that Burke paleontologists were able to identify the species, Crassatellites conradiana. These clams lived in relatively
shallow water (less than 300 feet deep). Photo by Burke Museum.

In the end, all that hard work paid off. Washington is now the 37th state where dinosaurs have been found!

“The fossil record of the west coast is very spotty when compared to the rich record of the interior of North America,” said Peecook. “This specimen, though fragmentary, gives us insight into what the west coast was like 80 million years ago, plus it gets Washington into the dinosaur club!”

Why did it take so long to find a dinosaur in Washington state? Dinosaurs are found in rocks from the time periods in which they lived (240-66 million years ago). Much of Washington was underwater during this period, so Washington has very little rock of the right age and type. Because dinosaurs were land animals, it is very unusual to find dinosaur fossils in marine rocks—making this fossil a rare and lucky discovery.

The Burke Museum is the Washington State Museum of Natural History and Culture. Burke Museum paleontologists were issued scientific collecting permits by Washington State Parks prior to excavating the fossil. Fossil exploration and collection on state land is legal only with proper permits issued for legitimate scientific research. Any items discovered in permitted scientific exploration are considered publicly owned and remain the property of Washington State Parks collections. The fossil is held in trust by the Burke Museum on behalf of State Parks.Posted by Cathy Morris, Digital Communications

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